The present invention relates to an electron beam resist material and a method for forming a finely patterned resist layer on a substrate surface by using the electron beam resist material. In particular, the inventive method utilizes a quite unique compound not used heretofore for the purpose of fine patterning of a resist layer in the field of electronic industries.
As is well known, the manufacturing process of various kinds of electronic or semiconductor devices such as ICs, LSIs and the like involves a fine patterning of a resist layer on the surface of a substrate material such as a semiconductor silicon wafer. This fine patterning process is conducted heretofore by the photolithographic method in which the substrate surface is uniformly coated with a positive- or negative-tone photoresist composition to form a thin layer of the photoresist composition and patternwise irradiating the photoresist layer with actinic rays such as ultraviolet light followed by a development treatment to selectively dissolve away the photoresist layer in the areas exposed or unexposed, respectively, to the actinic rays leaving a patterned resist layer on the substrate surface. The thus obtained patterned resist layer is utilized as a masking in the subsequent treatment on the substrate surface such as etching.
While the above mentioned patternwise exposure of the resist layer is conducted traditionally with ultraviolet light, it is a trend in recent years that, along with the rapid progress of the electronic technology toward higher and higher degrees of integration in semiconductor devices, the patterning of the resist layer is required to have more and more increased fineness which can be accomplished only by using actinic rays having a shorter wavelength than the conventional ultraviolet light. Accordingly, it has now come into sight that, in place of the conventional ultraviolet light, electron beams, excimer laser beams and X-rays are used as the short-wavelength actinic rays.
As the principal ingredient in a resist material having sensitivity to electron beam irradiation, referred to as an EB resist hereinafter, proposals have been made heretofore for the use of an organic resinous material such as methacrylic resin-based, polystyrene-based and novolak resin-based ones. In the polystyrene-based negative-tone EB resist materials, for example, patterning of the resist layer is accomplished by the mechanism that irradiation of the resist layer with electron beams induces crosslinking or polymerization of the resin molecules so that the resist layer is made insoluble in a developer solution in the areas patternwise irradiated with the electron beams leaving a patterned resist layer on the substrate surface so that, as a natural consequence, the fineness of patterning cannot be finer than the molecular dimensions of the resinous ingredient. In the novolak resin-based EB resist materials utilizing the changes in the solubility behavior of the resist layer in an alkaline developer solution caused by the patternwise irradiation with electron beams, the molecular size of the resinous ingredient is the limiting factor on the fineness of patterning since dissolution of the resist layer in the developer solution proceeds with resin molecules as the dissolving units. Thus, it is accepted in the prior art that resolution of patterning cannot be finer than several tens of nanometers at the best because the molecules of the above mentioned resins mostly have a molecular size of at least a few nanometers. In the so-called chemical amplification type resist materials recently under development, furthermore, the patterning of the resist layer utilizes the mechanism involving diffusion of the reactive species generated by the irradiation through the resist layer, it is far from possible to obtain pattern resolution in the ten-nanometer order or finer. Accordingly, it is eagerly desired to develop an EB resist capable of giving a high pattern resolution of nanometer order fineness which would not be obtained with the above described prior art EB resist systems.
In the methacrylic resin-based positive-tone EB resist materials, on the other hand, the pattern resolution is not always under limitation by the molecular size of the resinous ingredient because the patterning of the resist layer is effected by the main chain scission of the resin molecules by the irradiation with electron beams so that a pattern resolution of fineness of about 10 nm has already been obtained but the effective fineness of the working resist layer cannot be so high because the resistance of the resist layer against dry etching is relatively poor so that the patterned resist layer cannot be used as formed as a masking resist against etching.
It would be a due guide principle therefore that the above mentioned defects and problems in the prior art EB resist materials could be overcome when the EB resist comprises, as the principal ingredient, a compound of a nanometer order molecular size having sensitivity to electron beam irradiation and capable of giving a layer having excellent resistance against dry etching.